FIG. 1 shows a Radio Base Station (RBS) 100, which is known to be functionally separated into separate parts:                A Radio Unit (RU) 102, which creates the analogue transmit RF signal from the BB signal to be fed to the antenna and digitizes the received RF signal.        A Digital Unit (DU) 104, also termed a Baseband Unit (BBU) or Main Unit (MU), which generates and processes a digitized baseband (BB) Radio Frequency (RF) signal.        
In a conventional mobile network, the antenna, RF equipment and the DU are integrated into a single network element and placed at the cell site. This requires power, real estate space, and relatively large cell towers. As cell sizes are getting smaller, more sites needs to be built and operated.
An option to address this issue is decoupling of the baseband processing function from the radio function, and location of the baseband processing function (DU) in a centralized site. RUs are placed in the remote antenna site and named as Remote Radio Units (RRU). Point to Point links are used for interconnection of DUs and RRUs.
An interface specification for communication between the DUs and RRUs is the Common Public Radio Interface (CPRI). In some examples, references to CPRI refer to CPRI Specification V6.0 (2013-08-30) Common Public Radio Interface (CPRI); Interface Specification. In CPRI standards reference, the DU 102 subsystem is named Radio Equipment Control (REC) and the RRU 104 subsystem is named Radio Equipment (RE), respectively.
It has been considered to provide a number of RRUs, distributed over a geographical area. Several DUs can be collected in centralized pool (sometimes referred to as a “baseband hotel”) to control a large number of RRUs distributed over a geographical area. This network architecture may be referred to as Coordinated RAN, Cloud RAN or Centralized RAN (C-RAN).
In said C-RAN context, CPRI traffic must be transported over long distances between the DU site and the RRU site. This segment of the mobile traffic transport may be referred to as fronthaul. CPRI traffic has stringent latency, jitter and symmetry requirements. In particular: overall latency over the network is typically required to be within about 100 μs, asymmetry between the forward and reverse transmission shall be controlled in the order of a few tens of nanoseconds, and jitter of a few parts per billion (ppb) is also imposed by the CPRI specification.
With these tight requirements, transport of CPRI over traditional packet networks would be unfeasible due to, for example, Packet Delay Variation (PDV) and asymmetry which typically affect this environment.